The present invention relates to a high molecular weight polyester for use in coating applications.
It is known in the art that polyester resins such as the alkyds and the so-called oil-free saturated polyesters can be deposited on substrates and cured with curing agents as coatings with good hardness and chemical resistance. However, such coatings are generally low in extensibility which restricts their usefulness. Such coatings do not have sufficient elasticity and long term flexibility to make them suitable as coatings for elastomeric substrates such as are used for automobiles.
Modern automobiles use significant and increasing amounts of plastic and elastomeric components in their manufacture which has increased the demand for coatings with a high degree of elasticity as well as toughness and durability. Examples of suitable elastomeric coatings are those which contain as the resinous component poly(ester-urethane) polyols cured with an aminoplast such as described in U.S. Pat. No. 3,962,522 to Chang and Hartman. However, these coatings are expensive to make because of the diisocyanate component. Polyesters cured with an aminoplast are an economical alternative to the poly(ester-urethanes) cured with an aminoplast; however, as mentioned above, they have not generally been satisfactory. Besides not having a high degree of elasticity nor flexibility upon exposure to the atmosphere, polyesters do not provide good metallic pigment pattern control which is necessary for metallic colors which are currently so popular in automotive paints.